Hang gliders and hang gliding are as old as man's first dreams of simulating the flight of birds. However, it is only recently that successful hand gliders have burst upon the horizon, made possible by the availability of a unique combination of high strength synthetic resinous fabric and film, and light-weight high-strength rigid structural components.
A hang glider is defined as: "An un-powered single place vehicle whose launch and landing capability depends entirely on the legs of the occupant, and whose ability to remain in flight is generated by natural air current only" (see FAA Advisory Circular 60-10 published May 16, 1974). It is such a craft, which is powered by an engine now combined surprisingly effectively with a reduction drive unit, which is the subject matter of this invention.
The essential requirements of any winged aircraft in the 25-35 mph (miles per hour) range have been generally ignored since the Wright brothers powered a low-speed glider. This attitude is understandable because, logically, having learned to power a craft, the goal to be attained was ever-greater speeds. Subsequent world wars placed an additional premium on speed, and as a result, data on low-speed, winged, powered aircraft are virtually non-existent.
Since reliance for relatively safe flight solely upon the vagaries of air currents presents an undesirably high level of risk, it was inevitable that this reliance be better founded. An obvious way of providing a more reliable source of air currents is to power a hang glider with a small engine, and this has been done. Particularly in those parts of this country where the land stretches flatly to the horizons, powered or motorized hang gliders have been used in which an engine directly drives a propeller which is mounted on the crankshaft of the engine. These direct-drive powered hang gliders are not without problems. In simple terms it might be said that known, powered direct-drive hang gliders have delicate handling characteristics because they fly at near-stalling speed, a condition arising from the limited thrust of the necessarily small engine. To maximize thrust, a directly driven propeller is rotated as fast as the small engine will permit. Because of the weight limitation of a hang glider, it must be powered by a light-weight two-cycle internal combustion engine operating in the range from about 6500 revolutions per minute (rpm) to about 10,000 rpm. The handling problem of a powered hang glider is particularly acute at lift-off because, though the relatively small diameter propeller of a direct-drive engine rotates at high speed, there is insufficient reserve thrust to provide an adequate safety margin at lift-off. In other words, a small diameter direct-drive propeller does not provide sufficient thrust to make a quick and controlled transition from launch speed to the minimum safe control speed for the craft. Though this problem would appear to lend itself to a simple substitution involving using a more powerful engine, the fact is that such a substitution is impractical. The weight of a two-cycle engine having a rated brake horsepower greater than about 15 HP, even if cast from aluminum or other light weight alloy, is too great. Since a hang glider must be foot-launched and foot-landed, the critical weight of an engine to power it, is limited to 20 pounds (lbs). Thus, in powered hang glider design, the weight of an engine is essentially constant. Because launching a hang glider is accomplished by a person lifting it up and running with it to commence to lift off the ground, the weight of the enigne and hang glider together should not exceed 100 lbs.
The power of the two-cycle engine and its weight are critical factors because there is no known engine obviously suitable for the purpose of powering a hang glider, which engine can provide substantially greater power per pound weight, so as to rotate a large propeller slowly, without using a reduction-drive. These critical factors necessitate present direct-drive driven hang gliders to be operated without a muffler on the engine, so as to provide a reasonable margin of safety in making the transition from launch speed to crusing speed. Such an un-muffled engine requires the occupant pilot to use ear plugs or the like. It should also be recognized that the noise generated by a relatively small, high-revving propeller is so great that ear protective devices would be necessary even if the engine was quiet. A slow-revving propeller in the range from about 0.9 meter (m) to about 1.4 m, revolving at a speed in the range from about 2500 rpm, but below 5000 rpm, is relatively quiet. Because the engine provides more usable thrust with a large propeller driven with a reduction-drive unit, the engine may be adequately muffled so that the hang glider may be flown without ear plugs.
Recognizing that the cruise speed of a powered hang glider is in the range from about 25 to 35 miles per hour (mph) with a maximum speed of about 40 mph, it is essential that the transition from ground running speed of about 8 to 10 mph, to cruise speed, be made as quickly as possible. Since the stall speed is about 20 mph, it will now be appreciated that it is desirable to have as much reserve thrust as possible above a level required to maintain the hang glider in sustained flight. It is this reserve thrust which is lacking in a direct-powered hang glider.
Despite the inadequacies of direct-drive powered hang gliders, those skilled in the art have continued to use them, methodically attempting to overcome the problems . . . but with little success. The powered hang glider of this invention provides an effective solution to the problem of direct-powered hang gliding.